1. Field of the Invention
The present invention relates to a boosted voltage generator, and more particularly to an improved boosted-voltage synchronizing generator for decreasing power consumption in proportion to a bandwidth, and for outputting a stable and amplified voltage by employing an externally applied clock signal as a voltage pumping signal.
2. Description of the Prior Art
As shown in FIG. 1, conventional voltage generators include: an internal oscillator 10 outputting an internal oscillation signal OSC; a pump controller 20 receiving the internal oscillation signal OSC and an external control signal CON, and outputting a charging control signal QCON, a precharging control signal PCON and a charge transfer control signal CCON; a pumping capacitor C1 formed by a MOS transistor Q1 receiving the charging control signal QCON at a node connecting its source and drain and charging a node N connected to its case; a precharge circuit 30 receiving the precharging control signal PCON and an externally-supplied supply voltage Vdd and clamping the potential at the node N so that it does not fall below a predetermined voltage; an NMOS charge transfer transistor Q2 for regulating transfer of the voltage at node N to a load 50; and a charge transfer circuit 40 receiving the charge transfer control signal CCON and outputting a pumping control signal TRN for controlling the charge transfer transistor Q2.
The operation of the above-described boosted voltage generator according to the conventional art will now be described with reference to FIGS. 2A through 3.
First, the internal oscillator 10 generates the internal oscillation signal OSC having a predetermined cycle as shown in FIG. 2A. The frequency of the internal oscillation signal OSC is fixed in accordance with a delay and feedback circuit (not shown) consisting of an odd number of inverter chains (not shown) and transistors (not shown).
The pump controller 20 receives the internal oscillation signal OSC output from the internal oscillator 10 and the externally applied control signal CON, and generates the charging control signal QCON, the precharging control signal PCON and the charge transfer control signal CCON.
The charging control signal QCON, as shown in FIG. 2B, is applied to the pumping capacitor C1 to thereby charge the node N. The precharge circuit 30 receives the precharging control signal PCON and carries out a clamping operation so that the voltage at node N does not fall below the level of supply voltage Vdd. Therefore, the voltage PRC on the node N oscillates between the supply voltage Vdd and a boosted voltage Vpp, where the boosted voltage Vpp is defined by the sum of the supply voltage Vdd and the threshold voltage Vth of the MOS transistor Q2.
The charge transfer circuit 40 receives the charge transfer control signal CCON and generates the pumping control signal TRN which has a phase identical to that of the voltage PRC charged on the node N. The pumping control signal TRN is applied to the gate of the charge transfer transistor Q2, which outputs the high voltage level of the voltage at node N (e.g., the boosted voltage Vpp) by the pumping capacitor C1 to the load 50.
The boosted voltage generator according to the conventional art employs the internal oscillation signal OSC that is output from the internal oscillator 10 and that has a fixed frequency range. Therefore, the range of operation of the boosted voltage generator may be too narrowly limited by the fixed frequency range of the internal oscillator 10, rendering the boosted voltage generator unable to compensate for current Ipp consumed by the load 50 when outside the limited operating range of the boosted voltage generator. For instance, at frequencics above the limit of the boosted voltage generator, which limit is established based on the internal oscillation signal OSC, current consumed by load 50 is not compensated, rendering data unrecognizable.
By contrast, when the highest frequency of the boosted voltage generator is increased too significantly based on the frequency of the internal oscillation signal OSC, the power consumption tends to increase. For example, numerous problems are experienced when the load 50 represents a synchronous semiconductor memory device to be driven with boosted voltage Vpp output from the boosted voltage generator according to the ccnventional art.
First, the boosted voltage Vpp output from the boosted voltage generator according to the conventional art must drive both the gate of an NMOS pass transistor (not shown) of a memory cell, and the gate of a full-up NMOS transistor (not shown) of an output buffer. Because an appropriate level for the boosted voltage is different for each of these gates, it is difficult to optimize the level of the boosted voltage. For instance, an appropriate boosted voltage level for a memory cell is xe2x80x98Vdd+2Vthxe2x80x99 while an appropriate boosted voltage level for an output buffer is xe2x80x98Vdd+Vthxe2x80x99.
Second, a data signal in the output buffer is synchronized and changed between high and low potential levels in accordance with a clock signal. When a data signal is changed to a high potential level, the boosted voltage Vpp output from the conventional boosted-voltage generator is applied to the gate of a full-up NMOS transistor (not shown) to perform a logic operation of a level shift circuit. As a result, a band width variation of a clock signal in a circuit related to the synchronously operating output buffer is so large that variation of a driving current Iss flowing through the boosted voltage generator becomes large relative to the band width. Because the conventional boosted-voltage generator operates based on a fixed frequency oscillation signal output from the internal oscillator 10, the internal oscillator 10 must have a wide band width to allow for synchronization over a wide range of band widths. However, as shown in FIG. 3, since the internal oscillator has a fixed frequency, its band width is necessarily limited. Therefore, the driving current Iss of the boosted voltage generator may exceed the current Ipp flowing the load 50, effectively causing increased power consumption.
It is an object of the present invention to improve upon the conventional generator described above.
It is also an object of the present invention to provide a synchronized boosted voltage generator capable of decreasing power consumption by making a bandwidth of a clock signal applied to the boosted voltage generator proportional to a bandwidth in terms of consumption current, and to provide a boosted voltage generator having a high bandwidth.
To achieve the above and other objects, there is provided a synchronized boosted voltage generator which includes a pump controller for receiving an externally applied clock signal and an externally applied control signal, and outputting a charging control signal, a precharging control signal and a charge transfer control signal, a pumping capacitor for receiving the charging control signal and charging a node, a precharge circuit for receiving the precharging control signal and clamping a potential on the node so as not to fall below a predetermined voltage, a charge transfer transistor for transferring to a load the potential charged on the node and the pumping capacitor, respectively, and a charge transfer circuit for receiving the charge transfer control signal, anal for outputting a pumping control signal for controlling the charge transfer transistor in accordance therewith.